Trevor Graham, the coach of disgraced sprinter Justin Gatlin, is under investigation by athletics authorities.

The International Association of Athletics Federations (IAAF) is joining with the United States Anti-Doping Agency (Usada) to investigate Graham.

A number of Graham's athletes have been found guilty of using drugs.

"If evidence exists that he has engaged in doping practices in breach of IAAF rules, disciplinary proceedings will be initiated against him," the IAAF said.

"The IAAF remains totally committed to the fight against doping.

"In order to defend the credibility of our sport, we will engage all our efforts to defend the majority of athletes who are clean, against athletes, coaches, managers or any other support personnel who break our anti-doping rules."

World and Olympic 100m champion Gatlin is facing a lifetime ban after testing positive for elevated levels of testosterone.